Ribbon cartridges containing inked ribbons for use in powered typewriters and the like, have gained wide acceptance because of the ease of installing such cartridges and because of their inherent cleanliness. Often, such ribbons are of the single pass type, i.e., are not reuseable, wherein the cartridge is, after use, discarded. To manufacture such disposable cartridges which reliably serve their purpose at an economical price is a challenge. With the emergence of higher and still higher speed typewriters/printers, the physical demands made on such cartridges are increasing and the problem of making an economical and reliable cartridge is compounded.
Among the problems encountered in ribbon cartridges is that of maintaining the span of ribbon external to the cartridge at a desired length. If too much ribbon were present, it could become ensnarled with the typing/printing mechanism. To prevent this from happening, provision for stopping or braking both the supply and takeup must be provided. One advantageous method of achieving this is described in U.S. Pat. No. 4,013,160, assigned to A. B. Dick Company, the assignee of the present invention, which patent issued on Mar. 22, 1977, in the names of Paul S. Colecchi, the present inventor, and Cezary Kotecki. The present invention, although capable of a broader application, will be described in the environment of the cartridge described and claimed in that patent.
While constant friction, even aided by spring pressure, may be adequate in some applications, such as shown in U.S. Pat. No. 3,974,906, the increased stress and vibrations resulting occasionally on higher speed powered typewriters and the like, as, for example, result from a full carriage return, make this approach unacceptable. The force necessary to hold the ribbon under these circumstances (which must be overcome to advance it) would require an excessively thick or strong ribbon or would run the danger of breaking or tearing the ribbon.
While mechanical hub rims and lever interlocks, such as shown in U.S. Pat. No. 4,010,839, may be effective, they do not necessarily prevent overruns of a supply spool caused by tightening of the ribbon on its hub, and they require provisions of extra and relatively expensive parts.